The inventive concept relates to a method of operating a memory device and memory system.
Memory devices are classified as volatile memory devices and nonvolatile memory devices. Volatile memory devices lose stored data when the power supply is turned off, or otherwise interrupted. Examples of volatile memory devices include static random access memory (SRAM) devices, dynamic random access memory (DRAM) devices, and synchronous dynamic random access memory (SDRAM) devices.
Nonvolatile memory devices retain stored data even when the power supply is interrupted. Examples of nonvolatile memory devices include read-only memory (ROM) devices, programmable read-only memory (PROM) devices, erasable programmable read-only memory (EPROM) devices, electrically erasable programmable read-only memory (EEPROM) devices, flash memory devices, and resistive memory devices (e.g., phase-change random access memory (PRAM) devices, ferroelectric random access memory (FRAM) devices, and resistive random access memory (RRAM) devices).
A flash memory device may perform an electric erase operation on a block-by-block basis and a program operation on a bit-by-bit basis. Threshold voltages of programmed memory cells included in a flash memory device may change due to various causes, including floating gate coupling and charge loss over time. Changes in the threshold voltages of the memory cells can undermine the reliability of read data.